The Year 2000 Brings Problems to the UK Motorist.......
A great deal of information is bandied about over unleaded and lead fuel. Quite honestly, if an engine has done over 100,000 miles, and is in good condition, it will easily accept an unleaded head. The compression ratio will not change that much, and to say the engine needs an overhaul to have an unleaded head fitted smacks a bit of the garage chap offering to fit a new bit when it is not required. For instance, there are many MGB's about that came from the USA as re-imports to the UK, that are running with unleaded heads already, as certain states insisted all such cars were to be fitted. The owners probably not even aware their car is so modified, these will have done well over 100,000 miles.
The fitting of valve seat inserts is not a new engineering area. Anyone who looks inside their workshop manual will see that (especially on the Riley 4/68, 4/72 , Mk3 and Mk4 Magnette, etc with the 'B' series engine,) there is a whole section on fitting seat inserts. Why is this now being treated as if its all 'NEW'? Valve seat inserts have been fitted since the first engines ran, to recover what would otherwise have been scrap. The reason the cylinder heads needed inserts was because exhaust valve have been burning out seats since then!!
To get round the problems of the exhaust valve burning out its seat car manufacturers fitted hardend steel inserts, or put a big removeable nut over the valve on sidevalve engine so access could be had to regrind them in....the infamous 'De-coke'.
Engine makers need to make profits,like any manufacturer, so they use the cheapest materials they can. As more power was rung from the poor car engine, so up went the costs of building it. Not only were hard steel seats needed, so were phosphor-bronze exhaust valve guides, to withstand the heat and wear rates. On aircraft, the exhaust valve itself needed cooling, and was sodium filled. This was all in the mid 1920's by the way.Aircraft engines were streets ahead of the car engine by the 1930's, with superchargers, intercoolers, etc. As cost was not a worry, engines were made of magnesium alloy, a metal useless for valve seats. The Rolls Royce Merlin of WW2 fame is often quoted in sales literature,( usually involving tin pellets...) to say that on the Russian Front in WW2, the fuel was so bad tin pellets were used to increase the octane rating. This may be,or may not be, true. Alas the advert goes on to say that their product will protect exhaust valve seats in your classic car. Well, as the Merlin had hard steel inserts for valve seats, methanol to cool the cylinder block, and soduim filled exhaust valve stems, the comparison is very wrong. No way did the Merlin (Spitfire & Lancaster engine,) need any exhaust valve seats protecting. We are in the 1930's now by the way as far as the engineering of the engine is concerned.
As the ordinary car engine could not afford such luxury as the Merlin, (and other aircraft engines,) the petrol companies began to use Tetra-ethyl-lead as an additive. I can remember in the 1960's washing my hands in AVGAS high octane aircraft fuel, (for piston aircraft,...jets use Kerosine, or parrafin to you and I, ) to remove the oil, and my hands glistening white with the lead once the fuel dried........the more TET the higher the compression ratio, the more power. Back to the 1930's....as this TET improved the octane rating, so the car engines could have higher compression ratios, infact to get higher ratios the overhead valve engine surplanted the side valve unit, as this gave a more compact combustion chamber. As a spin off, the manufacturers found the TET acted as a lubricant to the exhaust valve seat and stem. This meant there was no need for expensive inserts or valve guides. These could all now be made of Grey Cast Iron, the cheap material used to cast the head. The TET acted as a constantly self-replacing metal gasket on the exhaust valve seat, it also helped the valve to pass its heat into the head more efficiently, so the valve need not be of such good grade steel, even less cost.
This happy result continued up until the numbers of cars meant there was a percieved pollution problem, and by the mid 1980's leaded engines were dead. Interestingly, Japanese cars and motorcycles, and Eastern-bloc cars, were always leadfree. Cars now had 9.5 to 1 and even 10 to 1 compression ratios, to get the best out of the high TET content petrol. Pre-WW2 cars had 6 to 1 or perhaps 6.5 to 1 if a sports car. Because of the pollution problems that seemed more political than reasoned, cars were to be fitted with catalytic converters. This changed the bad bits of the exhaust into carbon dioxide and water, (so adding to the Greenhouse effect?) Tetra Ethyl Lead is instant DEATH to a CAT, it ruins the very fine surface of expensive metals coated on the ceramic core, (rhodium, for instance,) so TET had to go. The CAT is also ruined by too much choke, burning oil, and being doused in cold water once hot enough to operate if you go through a puddle!!!!
The loss of TET in petrol means your 1960's classic car engine, if made of grey cast iron, with no inserts or special valve guides, will burn away the valve seat at a rather fast rate. Look upon it as a sand dune with a hard crust, then the wind breaks away the crust and simply blows away the sand. Your valve seat will overheat,as will the valve itself, until it is incandescent, and be burnt away,simply because the poor valve cannot get rid of the heat it lives in, (over 2000 degrees C.) It desperately needs a good seating in the head to pass the heat into it; if the seating is poor, then bye-bye valve. To make matters worse, the cooling of the area round the exhaust valve may not be as it was designed, as the 'internal hollows' of your engine rely on simple sand castings, not the most accurate method. The 'sand-core' can vary quite a lot from day to day in a foundry, where your engines head was born,so some engines may have good cooling where the water can flow, other may be very marginal with stagnant areas of water. (Running-on is a good example..) Within the tolerances allowed by the car makers, suchminor differences in engines did not matter, until now!
Your MGA,MGB,MGC,Magnette, Midget, TA,TB,TC,TD,TF,YA, YB,1100/1300, Metro; or Riley 1500, 4/68, 4/72, using the XPAG,XPEG,BMC 'A','B' or 'C' series, engine has a grey cast iron cylinder head using a poor quality steel exhaust valve and a cast iron valve guide, as built. It must have hardend steel exhaust valve seat inserts fitted, and phosphor bronze valve guides, and ideally Nimonic alloy steel valves, or at least plated valve seat edges. If you use plated valves, you must NOT grind them in or you remove the hardend edges, use an old recut valve.The Rover V8 unit ( an ex-USA Buick small V8, ) is an aluminium alloy engine with steel inserts, as fitted to the MGB GT V8. I ran my P6B on unleaded fuel with no problems.
Back to catalytic converters...there are two types, both can only be used with unleaded fuel, both need to get very hot before they work, (a problem for stop-start short journey motoring I fear.) One type is for normally aspirated engines, ( carbs,) the other is for fuel managed engines,( fuel injection.) The second type are more efficient but more delicate. They use a stainless steel shell containing a ceramic core of a matrix formation. They can obstruct the exhaust gas flow if they get coated too much, with engine exhaust deposits. The ceramic is coated with very expensive metals, such as palladium, platinum or rhodium, that acts as a catalyst to effect the nasty gasses, changing them chemically into carbon dioxide and water.The use of rhodium is interesting as this can be reclaimed from defunct nuclear power stations waste, though still an expensive task. One side effect is that if the petrol used is high in sulphur, then a Cat. will release this, thats the horrible pong you get when a new car passes you. The export MGB fitted with a CAT was that model destined for California, and it was fitted with a single Zenith Stromberg carb for easier fuel mixture control, from 1974. It is these 'rust-free' re-imported, California lead free cars I refer to above.
A bit more information for the data-hungry Farina M.G.and Riley owner.